Helium-neon lasers

Abstract

A stabilized helium-neon laser emits radiation in the ranges of ultra-violet, infra-red and visible other than red in at least two modes. A stabilizing system consists of an alignment heater (19) which bends the laser tubes toward optimum alignment, a coil heater (20) which cyclically varies the tube length and permanent magnets (24,25) which reduce instability of mode polarizations and to optimize relative intensities of the modes. The transmitted output is stabilized in frequency by control of the laser tube length, with the stabilization signal derived from the steady or varying intensity of intensities of one or both of two orthogonally polarized optical outputs. There are many potential uses for non-red helium-neon lasers in applications where non-red light is required, for example, in multi-wavelength interferometry.

What is claimed is: 
     
       1. In a helium-neon laser of the type emitting radiation in the ranges of ultra-violet, infra-red and visible, other than red light, said laser having a laser tube with a length and circumference, the laser tube emitting the radiation in at least two modes, a stabilising system including, in combination: a heating system means for supplying heat substantially uniformally along the length of the laser tube and asymetrically around the circumference of the laser tube, for bending the laser tube towards an optimum alignment;   a permanent magnetic field means for reducing instability of mode polarisations and to optimise relative intensities of the modes;   means for frequency modulation by cyclically varying the tube length; and   means providing active frequency stabilisation by control of the tube length, with a stabilisation signal derived from at least one of a steady, varying intensity, and intensities of at least two orthogonally polarised optical outputs.   
     
     
       2. A helium-neon laser as claimed in claim 1 characterised in that the tube length is cyclically varied by piezo-electric means. 
     
     
       3. A helium-neon laser as claimed in claim 1 characterised in that the tube length is cyclically varied by magnetic means. 
     
     
       4. A helium-neon laser as claimed in claim 1 characterised in that the tube length is cyclically varied by thermal means. 
     
     
       5. A helium-neon laser as claimed in claim 4 characterised in that the thermal means is effected by varying electric current in an electric supply to the heating system. 
     
     
       6. A helium-neon laser as claimed in claim 1 characterised in that the heating system includes a strip heating element extending along the length of the laser tube. 
     
     
       7. A helium-neon laser as claimed in claim 1 characterised in that the heating system includes a separately heated metal bar. 
     
     
       8. A helium-neon laser as claimed in claim 1 characterised in that the stabilisation signal is derived from a balance between the intensities of the orthogonal polarisations. 
     
     
       9. A helium-neon laser as claimed in claim 1 characterised in that the stabilisation signal is derived from a variation in intensity resulting from an imposed modulation of the laser tube length.